BACKGROUND: Mandibular angle osteotomy (MAO) is one of the most effective ways to correct square facial contours. With the development of Artificial Intelligence (AI) technology, particularly in medicine, more patients are seeking medical queries from online websites. This study compared the performance of 2 AI platforms, ChatGPT-4o and DeepSeek in answering questions about MAO. METHODS: Twenty frequently asked questions about MAO were selected and answered by ChatGPT-4o and DeepSeek. The responses from 2 platforms were graded by 9 experienced craniomaxillofacial plastic surgeons from 2 different hospitals. The relevance, accuracy, completeness, and readability of responses were evaluated. The 20 questions were divided into 4 categories: general conception, surgery process, complication, and other topics. Statistical analysis, including the 2-sided t test and Kruskal-Wallis test was applied to compare metrics. RESULTS: Both ChatGPT-4o and DeepSeek provided high-quality information about MAO. However, ChatGPT-4o outperformed in giving more thorough answers (4.4945±0.03089 vs. 4.4315±0.02519, P=0.048), and DeepSeek outperformed in giving answers more easily to read (4.2960±0.04717 vs. 4.1965±0.03986, P=0.026). Also, although ChatGPT performed well in answering all kinds of questions, DeepSeek had weak performance in answering questions regarding surgery process of MAO. CONCLUSIONS: Both platforms offered reliable information. Compared to DeepSeek, ChatGPT-4o provided more thorough responses and was more aligned with clinical practice. This study discovered the potential of AI platforms in addressing patient education and providing medical information in craniomaxillofacial plastic surgery field.